FECHNER'S COLOURS

Fechner's colours: translation

   Also known as subjective colours, illusory colours, and flicker colours. The eponym Fechner's colours refers to the German psychologist Gustav Theodor Fechner (1801-1887), who in 1838 published an account involving the creation of illusory colours with the aid of flickering monochromatic light. In this paper Fechner describes how coloured rings appear when a white disc with six black sectors ofincreasing size is rotated at about 30 revolutions/s. While one would expect to perceive six concentric rings of grey with an increasing saturation, this actually results in pale bands of brown-red, red, green, blue, and bluish purple. When rotated in the opposite direction, the same colours appear in reverse order. These illusory colours are referred to as pattern-induced flicker colours (PIFCs). The underlying effect is known as the Prévost-Fechner-Benham effect. The neurophysiological correlates of this effect are not entirely understood, but it is believed that both the retina and the primary visual cortex play an active part in the mediation of the ensuing illusory colours. A variant of the device used by Fechner is known as *Benham's top. Fechner's colours are classified as a * physiological illusion.

   References

   Fechner, G.T. (1838). Ueber eine Scheibe zur Erzeugung subjectiver Farben. Poggendorffs Annalen der Physik und Chemie, 45, 227-232.

   Ninio, J. (2001). The science ofillusions.Trans-lated by Philip, F. Ithaca, NY: Cornell University Press.